In an endeavor to lessen the weight of passenger cars and to reduce car body rusting, it has been proposed to expand the use of fiberglass reinforced polyester (FRP) panels to replace some or all of the metal body panels currently being used in car bodies. In the use of the FRP panels, the panels which form the completed body customarily are joined together with an adhesive bonding system.
To be satisfactory, the adhesive system must produce a strong bond (35 kgf/cm.sup.2 minimum) within a relatively short period of time (desirably within about 7-8 minutes) at ambient production area temperatures (which normally range from about 20.degree. C. to 35.degree. C.) and withstand the relatively high temperatures developed within the engine compartment of modern cars.
The adhesive also must have sufficient resistance to flow during the time which elapses after application to the FRP panels and before it sets to resist flowing outside the prescribed "bond line" between the assembled panels even if the assembled panels are upended for movement to the next assembly point before the adhesive has had an opportunity to set.
One adhesive material which has been proposed for bonding FRP panels is based upon a polyurethane composition obtained by reacting together 100 parts of a polyester or polyether polyol or a polyesteramide with a molecular weight between 700 and 4500, 38 to 80 parts of an organic polyisocyanate, 5 to 200 parts of filler, a catalyst, and sufficient monomeric nitrogen containing polyol having from 3 to 6 hydroxyls to react with the excess polyisocyanate material in the system (see U.S. Pat. No. 3,812,003).